By Stephen Fisher.

The collective intelligence of political journalists suggests that the House of Commons is likely to vote against the prime minister’s Brexit deal when it comes to a “meaningful vote” in December. Supposing this happens, what next?

The UK would, by legal default, be heading towards a no-deal Brexit. Although the government would have till mid-January to say how it intended to proceed, Mrs May would most likely want to move quickly, given the risk of a no-confidence vote from both inside and outside her party.

Waiting to see if a market crash sways MPs is unlikely to be an option. If the outcome of the parliamentary vote is as clear as many commentators suggest it will be, then the markets will have already priced it in. That is not to say that the markets will assume failure of the meaningful vote automatically means a no-deal Brexit, just that the markets are unlikely to move much if the outcome is as is widely anticipated.

Simply announcing that she will seek further concessions from Brussels would be unpersuasive. What makes her deal unpopular with the DUP and many of her backbenchers are structural features that were already much discussed. The EU are unlikely to be willing to make sufficient concessions, especially not on the current timescale. Substantial further negotiations would probably require an extension to the Article 50 process, which the EU have said would only be granted if there was a “fundamental change” in the political situation in the UK. (A referendum would be such a change.) What’s more, MPs are unlikely to think that the Theresa May would be the best person to achieve a better deal given they are unhappy with her previous efforts.

The prime minister has said that a no-deal Brexit would be “a bad outcome for the UK”, and also that she believes, with her “head and heart” and “every fibre of her body”, that the deal is, “in the best interests of our entire United Kingdom.” If this is really how she feels she should want to ask the people to back her deal in a referendum to force parliament’s hand. May has previously ruled out a referendum, but she also ruled out a general election in 2017 and called one anyway.

Even if she does not really feel so strongly in favour of her deal, calling another referendum still looks like it would be the most palatable of the options that would immediately be available. Calling a general election would be much riskier. Resigning would be a dereliction of duty without any obvious indication that any other prime minister would yield a better outcome for her party or the country. She would have no credible argument for trying to unilaterally revoke Article 50: it is not what she wants, it may not work and it would provoke a major legitimacy crisis. If she calls and fails to deliver a referendum at least she will have taken every opportunity to avert a no-deal Brexit.

Remain must be on the ballot to have any hope of parliament approving legislation for a referendum and the EU27 granting the necessary extension to the Article 50 process. A referendum would take a long time to set up and run. Avoiding or rescheduling the European Parliament elections would be a problem, but, as the UCL Constitution Unit have pointed out, there are solutions.

The prospect of parliament voting for a referendum on a deal they had just voted down would be perverse, but nonetheless it is highly likely that there would be a majority for such a referendum from a coalition of MPs loyal to the prime minister and Remain supporting MPs wanting a people’s vote.

The latter group include Liberal Democrat, Green, Scottish and Welsh nationalist, and a large number of Labour MPs who would be willing to rebel. Faced with a bill for another referendum, the Labour leadership would come under severe pressure to support it from their MPs, members and voters; all three groups are mostly made up of Remainers.

Labour’s current policy is to seek a general election and only consider other options afterwards. However, fighting, and even winning, a general election before March is not clearly in Labour’s interests. It would be hard for the leadership to maintain their pro-Brexit stance or justify a change. Unless they won an outright majority they might have to permit another Brexit and/or Scottish referendum to govern. In government, Labour would be unlikely to be able to negotiate a very different deal and they presumably do not want to preside over a no-deal Brexit.

If Labour had urgently desired a general election they could long ago have called a vote of no confidence. They could call one tomorrow to take advantage of the rift between the DUP and Conservatives. Calling for a general election to be held less than three months before Brexit day would look reckless. Electioneering over Christmas is still less of a cheery prospect.

Perhaps for this or other reasons, John McDonnell has recently indicated that he thinks a referendum is more likely than a general election. That suggests, if the PM moves quickly enough towards a referendum, Labour would not call a vote of no confidence.

There would be a greater risk to the PM of a leadership challenge from her own MPs in the European Research Group (ERG). Even though a Tory leadership election, less than four months before a no-deal Brexit for which the country is ill prepared, would be reckless and unedifying, there are Tory MPs who would consider it a worthwhile attempt to block a referendum that might derail Brexit.

Would it succeed? Even though ERG efforts fizzled out this week, they may very well succeed in ousting the Theresa May from the Conservative party leadership if she tries to call a referendum next month. But that on its own would not stop a referendum. Theresa May could continue as prime minister until the party chose a new leader, and that would take time enough for a referendum bill to pass through parliament. Remain supporting Conservative MPs could ensure that there were at least two candidates to contest a lengthy campaign for the membership vote.

So there is a good chance that if Theresa May calls a referendum she will lose the premiership in the process. That may not be much of a deterrent for her. Many do not expect her to survive as leader until the scheduled 2022 election, or even past the end of 2019 if the UK leaves the EU in March. She would not be cutting short her tenure by much, and she would be doing it while fighting for what she says she believes is in the national interest.

Some would argue that the prime minister was disingenuous. As a former Remain voter, Theresa May might well be relatively relaxed about the possibility of the country voting to stay in the EU, but, perhaps crucially politically and for her legacy, that would be incidental. The primary purpose of her referendum would be seeking support for her deal.

If current opinion polls are anything to go by then the deal would lose to Remain in a referendum, or to both Remain and no-deal if all three options are on the ballot. It would probably be politically expedient to have all three options on the ballot given the current popularity of no-deal among Leave voters.

While the scenario I have portrayed is the most likely route to a referendum, there are others. A referendum, one way or another, is reasonably likely because of the plausibility of different routes. Ultimately if the meaningful vote goes against the deal next month, as many expect it to, the two most likely eventual outcomes become Remain (after a referendum) or a no-deal Brexit (either after a referendum or, more likely, by default).

My argument has thus far assumed that Theresa May will act in what, ostensibly, she thinks is in the national interest. Suppose instead that she wants to act in the medium-term interests of her party. In which case, the question she would have to ask herself is how this is all going to look at the time of the 2022 general election. Would the Conservatives at the polls be punished more for an economically damaging no-deal Brexit (assuming she believes it would be damaging), or more for selling out Leave voters with a referendum that resulted in a Remain vote?

There is no clear answer to this question. What the Conservatives ought to bear in mind is that there is no clear precedent for voters re-electing governments out of thanks for disaster averted. Given the electorate did not even reward Churchill for winning World War II, there is little reason to expect the Tories to win re-election out of gratitude for avoiding a no-deal Brexit; especially not if opinion polls continue to show that Leave voters do not expect a no-deal Brexit to be a bad outcome. If there is harm to be avoided from a no-deal Brexit, it might be in the national interest to avoid it but not necessarily in the Conservative party’s interests.

Since re-election for the Tories after twelve years in power would be a difficult prospect even in easier circumstances and because the Brexit process might well shape the way voters view parties well beyond the next election, the Conservatives also face a longer term choice between whether they want to be seen primarily as a centre-right party that knows how to run the economy, or as the party that achieved liberation from the EU.

Both electoral history and demographic trends suggest that the best long-term strategy for the Tories is to continue to try to be a competent centrist party. Those who see a bright future for national populism as an electoral strategy might advocate the long-term benefits of following through with a no-deal Brexit. Not least losing Northern Ireland and Scotland from the union could become an advantage to the Tories. Who knows to what heights the peaks of English nationalism may be whipped?